Further evidence has emerged that the Syrian Government is targeting opposition activists using a well-known remote access Trojan distributed through bogus Skype calls.

A blog this week by Mikko Hypponen of antivirus company F-Secure describes receiving the hard drive image of a Syrian dissident’s PC which turned out to have been infected with the widely-available ‘Xtreme RAT’, a backdoor tool for remotely controlling and accessing PCs.

The activist had become infected after accepting a file over a Skype session from a known contact which he believed would help him to hide his PC’s hardware MAC address from Government snoopers.

In fact the file, MACAddressChanger.exe, turned out to be malicious and the contact had already been arrested before the call, raising the likelihood that the Syrian Government was behind the attack.

“We have reasons to believe this infection wasn't just bad luck. We believe the activist's computer was specifically targeted,” concluded Hypponen after tracing the malware’s communication channel back to an IP address controlled by the Syrian national telecoms company.

Earlier in the year anecdotal reports emerged that the Syrian authorities were using Skype to attempt to penetrate opposition communications using different backdoors, with the Electronic Frontier Foundation (EFF) also reporting Xtreme RAT attacks.

The regime had previously resorted to the extreme measure of cutting off the Internet altogether but seems to have realised that surveillance offers greater intelligence possibilities.

As such the attacks depend on the PC being poorly defended or the user open to social engineering. The MACAddressChanger.exe and Xtreme RAT apps are easily detected by an antivirus programme that monitors IM. So far such tactics are aggressive rather than sophisticated.

Also this week, French researchers have gone public over a Skype security flaw that could compromise users' IP addresses they claim was reported to the company in November 2010. This hole remains unpatched.